1. Field of the Invention
The present invention relates to a dog clutch that transmits a torque between rotational members by meshing, and a differential gear including the dog clutch.
2. Description of Related Art
Some differential devices (differential gears) that allow a differential action between right and left wheels of a vehicle and distribute a driving force thereto include a dog clutch that restricts a differential action between rotational members that are rotatable relative to each other (for example, see Japanese Patent Application Publication No. 2003-322240 (JP 2003-322240 A), Japanese Patent Application Publication No. 2008-95711 (JP 2008-95711 A)).
A differential device described in JP 2003-322240 A is placed on a front-wheel side of a four-wheel drive vehicle, and includes an outer differential case and an inner differential case rotatable relative to each other. A ring gear is fixed to an outer periphery of the outer differential case, and a pinion shaft is fixed to the inner differential case. A pair of pinion gears pivotally supported by the pinion shaft, and a pair of side gears meshing with the pair of pinion gears with their gear axes being at right angles are stored inside the inner differential case.
When a dog clutch is operated, a relative rotation between the inner differential case and the outer differential case is restricted, and when the dog clutch is not operated, the relative rotation is permitted. The dog clutch includes a plunger that moves axially upon receiving a magnetic force of an electromagnetic coil, and a clutch member pressed by the plunger. The clutch member integrally includes a plurality of fan-shaped leg portions, and a plurality of meshing teeth meshing with the inner differential case, and is biased by a return spring in a direction to be separated from the inner differential case. The plurality of fan-shaped leg portions of the clutch member is inserted into respective fan-shaped holes of the outer differential case. A circumferential end surface of the fan-shaped leg portion and an edge of the fan-shaped hole, the edge being opposed to the circumferential end surface are inclined with respect to an axis direction in parallel to each other. With this configuration, the fan-shaped hole of the outer differential case and the fan-shaped leg portion of the clutch member constitute a cam mechanism, and the clutch member receives a pressing force in a direction to mesh with the inner differential case, due to a thrust of the cam mechanism.
A differential device described in JP 2008-95711 A includes a disciform ring gear having an insertion hole through which an axle is passed, a differential case fixed to a side face of the ring gear, and a pair of pinion gears and a pair of side gears stored in the differential case. Further, the differential device described in JP 2008-95711 A includes, as a configuration to restrict a relative rotation of the ring gear and the differential case with respect to one side gear: an actuator having a motor; a fork-shaped operation metal fitting that axially moves by the actuator; an annular differential lock slider that axially moves together with the operation metal fitting; a clutch member that receives an operation force from the operation metal fitting via a pressing spring placed between the clutch member and the differential lock slider; and a plurality of ball members provided between a body portion of the ring gear and the clutch member. The ball member is partially stored in a bowl-shaped recessed portion provided in the body portion of the ring gear and also partially stored in a bowl-shaped recessed portion provided in the clutch member. A ball cam mechanism is constituted by the ring gear and the clutch member.
The clutch member is biased in a direction to be separated from one side gear by a return spring placed between the clutch member and a spring receiving portion of the differential case. Further, the clutch member integrally includes a plurality of meshing teeth meshing with one side gear, and a plurality of lock pins inserted into to a plurality of operation holes provided in the ring gear, respectively. A tip end of the lock pin is fitted slidably in a pin hole of the differential lock slider. When the operation metal fitting axially moves due to an operation of an actuator by a normal rotation of an electric motor, the clutch member is pressed against the side gear by the pressing spring, and the ball cam mechanism operates due to a relative rotation between the clutch member and the ring gear. Then, the clutch member is more strongly pressed against the side gear by a thrust of the ball cam mechanism, so that a plurality of meshing teeth of the clutch member meshes with the side gear.
As such, in the differential device described in JP 2008-95711 A, the clutch member is pressed against one side gear via the differential lock slider and the pressing spring due to the normal rotation of the electric motor, and the ball cam mechanism operates so that the clutch member meshes with the one side gear. Further, when the electric motor is reversed, the clutch member is separated from the one side gear, so that the clutch member is disengaged from the one side gear.